This invention relates to a circuit arrangement for carrying out battery saving operation and, in particular, to a circuit arrangement for use in a radio receiver, such as a portable receiver, driven by a battery.
A portable receiver often comprises a phase-locked loop circuit which will be called a synthesizer hereinunder. As known in the art, such a synthesizer can be used as a local oscillation circuit and comprises a voltage-controlled oscillator, a phase detector, and a reference oscillator. In a portable receiver of the type described, it is preferable that battery saving operation can be carried out during a waiting or standby operation for a call so as to save electric power consumption. However, existence of the synthesizer makes it difficult to carry out the battery saving operation. More particularly, let the synthesizer be repeatedly put in an intermittent active state and an intermittent inactive state during the battery saving operation. In this event, the synthesizer should be locked within the intermittent active state. Otherwise, the portable receiver would be wrongly operated. However, a long time must inevitably be wasted so as to put the synthesizer in a locked state in a usual manner.
A conventional circuit arrangement is proposed which comprises a synthesizer operable in cooperation with a power source circuit and a control circuit for controlling the power source circuit to make the synthesizer carry out the battery saving operation. More specifically, a continuous source voltage is supplied from the power source circuit to a voltage-controlled oscillator of the synthesizer during the battery saving operation while an intermittent source voltage is delivered to the remaining elements, such as a reference oscillator and a phase detector, under control of the control circuit during the battery saving operation. As a result, the phase detector is intermittently operated to intermittently detect a phase difference between a reference signal and an oscillation signal which are given from the reference oscillator and the voltage-controlled oscillator, respectively.
With this structure, the phase difference may widely be varied each time when the phase detector is intermittently energized by the intermittent source voltage. Such a wide variation of the phase difference results in an excessive fluctuation of the oscillation signal.